Most patients with small intestinal neuroendocrine tumors (SI-NETs), also referred to as midgut carcinoids, present with systemic disease at the time of diagnosis with metastases primarily found in regional lymph nodes and the liver. Curative treatment is not available for these patients and there is a need for novel and specific therapies. Engineered oncolytic viruses may meet the need and play an important role in the future management of SI-NET liver metastases. This review focuses on adenovirus as the oncolytic anti-cancer agent and its potential curative role for SI-NET liver metastases, but it also summarizes the use of oncolytic viruses for NETs in general. It discusses how specific features of neuroendocrine cell biology can be used to engineer viruses to become selective for infection of NET cells and/or replication within NET cells. In addition, it points out the advantages and shortcomings of using replicating viruses in the treatment of cancer and addresses research fields that can increase the efficacy of virus-based therapy.